This invention relates generally to continuous process control. In particular, this invention relates to management of analogue signals for digital process control.
It is known to effect control of processes by programmable digital control. Unlike purely analogue control circuits, a particular control algorithm can be represented by the steps of a program to be executed by the programmable control. Therefore, a single programmable control may be used to control totally independent and unlike processes without resort to unique circuitry.
As a practical matter, process control generally requires that plural process parameters be monitored to produce a desired value of a single control signal. For example, in servo mechanism control two channels of position feedback signals may be used to produce a single control signal. However, when a programmable device is used to control sampling of process parameters, the rate at which sampling must be effected imposes limitations on the program size or the number of process parameters which can be monitored. Further, the programmable control may not provide consistent sampling rates because of dynamically changing program execution times. The present invention overcomes these deficiencies of known systems for digital process control by providing for management of the analogue signals representing process parameters independently of the program execution of the digital control.